# Darkness before harvest

> The practice of keeping plants in total darkness for 24-72 hours before cutting to boost resin; GenetixBay rates it a Myth and runs a standing challenge against it.

- Canonical: https://genetixbay.com/knowledge/glossary/darkness-before-harvest.html
- Also written: dark period before harvest, 48 hours of darkness, 72 hours dark, pre-harvest darkness, dark treatment, lights off before harvest, 24-72 hours darkness
- Glossary category: Harvest, drying and curing · Evidence: Myth
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

Darkness before harvest means switching the lights off, or covering outdoor plants, for 24-72 hours before the chop. Proponents say the stress makes the plant pump out more resin or [THC](https://genetixbay.com/knowledge/glossary/thc.md). There is no credible evidence that it does.

## In practice

GenetixBay's advice is simple: keep the normal light schedule right up to harvest, and cut when the [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) say so. If a dark period helps with logistics (planning a lights-off harvest day, for example), treat it as logistics, not quality.

Why it makes no sense physiologically:
- the last weeks are when the plant packs on most of its final weight and resin;
- trichome resin is built from [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md), so switching it off takes away the supply;
- a day or two of darkness can't build meaningful new gland mass;
- lab-measured [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) increases from short dark periods haven't held up in controlled work.

## Don't confuse with

- **The flowering dark period**: the nightly 11-12 h dark that triggers and maintains flower.
- **Light deprivation**: covering outdoor plants to force early flowering.
- **Harvest window**: the right time to cut, judged by trichomes.

## Myth check

Myth, "complete and utter nonsense" in the founder's words. Why cut photosynthesis in the most critical part of the life cycle? The founder's standing challenge, open for 20+ years: find a peer-reviewed study (not a single-plant study, not biased or skewed) showing a benefit, and a 50-pack of seeds is yours, no questions asked. Nobody has claimed it. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md).

## Related terms

[Harvest window](https://genetixbay.com/knowledge/glossary/harvest-window.md), [Flushing](https://genetixbay.com/knowledge/glossary/flushing.md), [Photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md), [Trichome ripeness](https://genetixbay.com/knowledge/glossary/trichome-ripeness.md)

## Read more

- [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md)
- [Pre-harvest flushing: a myth that costs you yield and resin](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)

## Sources

1. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020